In this article, we will learn how to use the Primary Key constraint in SQL.
The PRIMARY KEY constraint is used to identify each record uniquely in a table.
Primary keys cannot contain NULL values and must contain UNIQUE values.
A table can have only one PRIMARY KEY but this primary key can be consist of single or multiple columns.
Please check How To Create Table Using Query In SQL, to get a brief description of the CREATE TABLE statement.
Example-1
The subsequent statement would create a PRIMARY KEY constraint on the “ID” column when the “Article” table is created:
CREATE TABLE Article ( ID int PRIMARY KEY, Title varchar(100), Author varchar(100), Views int );
Example-2
The subsequent statement would create a PRIMARY KEY constraint, which is made up of two columns (ID + Title) when the “Article” table is created:
CREATE TABLE Article ( ID int, Title varchar(100), Author varchar(100), Views int, CONSTRAINT PKArticle PRIMARY KEY (ID, Title) );
Please check How To Alter Table Using Query In SQL, to get a brief description of the ALTER TABLE statement.
Syntax
ALTER TABLE TABLE_NAME ADD CONSTRAINT CONSTRAINT_NAME PRIMARY KEY (column1, column2, ...columnN);
Example
The subsequent statement would add a PRIMARY KEY constraint on the “ID” column using ALTER TABLE statement:
ALTER TABLE Article ADD CONSTRAINT PKArticle PRIMARY KEY (ID);
Syntax
ALTER TABLE TABLE_NAME DROP CONSTRAINT CONSTRAINT_NAME;
Example
The subsequent statement would delete a PRIMARY KEY constraint named “PKArticle” using ALTER TABLE statement:
ALTER TABLE Article DROP CONSTRAINT PKArticle;
Also, check How To Use UNIQUE Constraint In SQL
In this article, we have to show Create and Used PIPE in angular
In this article, we have to show Create and Used PIPE in angular
In this article, we have to show Create and Used PIPE in angular
View Comments
Hi there, I found your web site by the use of Google at the same time as looking for a similar subject, your web site came up, it appears to be like great. I have bookmarked it in my google bookmarks.
Thank You